Optimising focusing parameters of very high energy electron beams for radiotherapy using Monte Carlo simulation

Very high energy electron (VHEE) beams, with energies of 100 MeV and above, offer favourable properties for radiotherapy, such as deep penetration depth and reduced sensitivity to tissue heterogeneity. Numerous simulation and experimental studies have investigated these properties for clinical application. In this study, we use Monte Carlo simulation using TOPAS to obtain the depth-dose profiles of VHEE beams with varying energy and focusing parameters. An empirical model is fitted to the central axis dose, yielding parameters that characterise the depth-dose profile. A linear interpolator then maps these fitting parameters to the focusing parameters, allowing us to identify the optimal focusing parameters. The results presented here are independent of the beamline and can therefore guide the design of a final focusing systems for VHEE beams.